You are right, I should be out skiing. It’s my favorite sport.
Two options that first came to mind:
The clip naturally does that in reverse. You could put it in FCP and then reverse it. If you go that route I would recommend the Nattress Reverse Filter that is free. https://www.nattress.com/
To make the change in the Particle Emitter. Select the Emitter and click on the Emitter tab. Change the life to around 5. (Life is how long the image will be on the screen. So once it is on the screen for 5 seconds it will disappear.) Mark a Birth Rate keyframe in the middle of the project, lets say 5 seconds. Jump another 15 frames down the time line and make another Birth Rate Key frame. Make the Value 4. This will start you out with a lot of people and drop them down to about 20 or so. Hope this helps.
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